Sensors are utilized in a variety of flow, humidity, pressure and temperature sensing applications. Flow sensors, for example, are utilized in a variety of fluid-sensing applications for detecting the movement of fluids, which may be in gaseous (e.g., air) of liquid form. One type of flow measurement, for example, is based on thermal sensors, which can also be utilized to detect the property of a fluid. Thermal sensors may be implemented, for example, on silicon in microstructure form. For convenience sake, and without limitation, the term “flow sensor” can also be utilized to refer to such thermal sensors. The reader will appreciate that such sensors may be also utilized to measure primary fluid properties such as temperature, thermal conductivity, specific heat, and other properties; and that the flows may be generated through forced or natural convection.
One example of a flow sensor is disclosed in U.S. Patent Application No. 20050022594, entitled “Flow Sensor with Self-Aligned Flow Channel,” to Aravind Padmanabhan, et al, which published on Feb. 3, 2005 and is assigned to Honeywell International Inc, and is herein incorporated by reference in its entirety. The device disclosed in U.S. Patent Application No. 20050022594 generally describes flow sensor having a substrate with a sensing element and flow channel aligned over the sensing element. The sensing element senses at least one property of a fluid. The flow channel is aligned by one or more guide elements formed in an alignment layer.
Another example of a flow sensor is disclosed in U.S. Pat. No. 6,871,537, entitled “Liquid Flow Sensor Thermal Interface Methods and Systems,” which issued to Richard Gehman et al on Mar. 29, 2005 and is assigned to Honeywell International Inc., and also incorporated herein by reference in its entirety. A fluid flow sensor described in U.S. patent described in U.S. Pat. No. 6,871,537 measures the thermal conductivity of a fluid. The sensor includes one or more sensing elements associated with a sensor substrate. A heater is associated with the sensor and provides heat to the fluid. A film component isolates the fluid from the heater and the sensor, and conducts heat in a direction from the heater to the sensor, thereby forming a thermal coupling between the sensor, the heater and the fluid, which permits the sensor to determine a composition of the fluid by measuring thermal conductivity thereof without undesired losses of heat in other directions. The film component can be configured as a tube or a flow channel.
An example of a humidity sensor is disclosed in U.S. Pat. No. 6,724,612, entitled “Relative Humidity Sensor with Integrated Signal Conditioning,” which issued to Davis et al on Apr. 20, 2004 and is assigned to Honeywell International Inc., and is also herein incorporated by reference in its entirety. The humidity sensor described in U.S. Pat. No. 6,724,612 relates to integrated relative humidity sensor that includes a planar humidity sensitive capacitor structure based on a thin porous platinum top plate, a humidity sensitive polyimide dielectric, and a metal (e.g., titanium-tungsten) bottom plate. Two capacitors are wired in series such that the metal bottom plates form the independent, electrically driven connections, and the thin platinum top layer is used to form the top plates and the floating series interconnection. Another example of a humidity sensor is disclosed in U.S. Pat. No. 6,867,602, entitled “Methods and Systems for Capacitive Balancing of Relative Humidity Sensors having Integrated Signal Conditioning,” which issued to Davis et al on Mar. 15, 2005 and is assigned to Honeywell International Inc., and also incorporated herein by reference in its entirety.
An example of a pressure sensor is disclosed in U.S. Pat. No. 6,945,118 entitled “Ceramic on Metal Pressure Transducer,” which issued to Maitland, Jr. et al on Sep. 20, 2005 and is assigned to Honeywell International Inc., and also incorporated herein by reference in its entirety. The device of U.S. Pat. No. 6,945,118 describes a pressure transducer apparatus based on a metal diaphragm molecularly bonded to a ceramic material to form a ceramic surface. A bridge circuit is connected to the ceramic surface of the metal diaphragm. An input pressure port for pressure sensing thereof is also provided, which connected to the metal diaphragm to thereby form a transducer apparatus comprising the metal diaphragm, the bridge circuit and the input pressure port.
It is often desirable to utilize more than one measurand in sensing applications. Typical sensor instrumentation utilized in medical applications, for example, use more then one measurand simultaneously to make calculations for measurements in the system. Usually the individual sensors utilized in such systems are either provided with calibrated or un-calibrated analog outputs or in the form of sensors with small-signal outputs, either of which may need to be conditioned and calibrated by the end user within the system.
In other cases the analog signals conditioned by the customer must pass through an analog-to-digital converter so that the output signals can be processed by the system which may be microcontroller-based. The most common measurands are pressure, flow, temperature or humidity. The output signals from the raw sensors are not linear and vary as a function of temperature. Variations must be taken into account and calibrated based on the accuracy required by the system.
Some sensors are packaged as raw sensors with simple electrical connection to the sensing element and others are packaged with compensation and/or amplification so as to simplify the electrical interface with a particular application. Few sensor outputs are presented through a digital interface which reduces the complexity of the customer interface requirements if it is a digitally processed system.
In order to improve such sensing applications and systems, it is believed that a modular sensing approach should be implemented as described in greater detail herein.